So the biotech's health falls to zero and he's bleeding. An alien attacks him again, and his defense roll is not enough -- it allows 3 damage to get through. That would normally kill him -- but one of the dice has a bolt, which has to be applied first. The bolt returns his health to 1, so he's no longer bleeding. But then the 3 damage kicks in and he's bleeding again.
So essentially the Biotech can't be killed until his defense roll doesn't show a bolt...?
Your interpretation is correct, The biotech has the worst armor , but Once he enters in bleeding it becomes Precious ! It was designed in this way cause the biotech Is "usually" the agent that heals the others, so he is quite more Difficult to kill (but still more than possible of course)